bystander wrote: ↑
Thu Sep 13, 2018 5:25 pm
How heavy is our Galaxy?
Astrobites | 2018 Sep 10
The mass of the Milky Way from satellite dynamics
Nora Shipp wrote:
Weighing our Galaxy is a difficult task. The Milky Way is a complicated mess of stars and gas, and – to make things even more difficult – the majority of our Galaxy is invisible in the form of dark matter
). Today’s paper states that current calculations of the mass range from about 500 billion to 2.5 trillion times the mass of our sun. The difference between these two huge numbers is only a factor of a few, but a precise measurement of the mass of the Galaxy is essential for understanding the physics of galaxy formation and for unraveling fundamental cosmological mysteries like the nature of dark matter.
This number is very important to pin down because our Galaxy is such a unique laboratory for studying the mysteries of the Universe. It is the only galaxy that we can observe from up-close, and thereby collect detailed information on the structure of a galaxy and the complicated physical processes that occur within it. This snapshot of a single galaxy can be generalized to overarching physical theories when combined with observations of distant galaxies and compared to theoretical predictions from numerical simulations. This generalization, however, depends on our ability to place the Milky Way in the context of the general galaxy population – and this requires a precise measurement of the mass of our Galaxy.
So, how is it possible to weigh a Galaxy from within? The authors of today’s paper measure the mass of the Milky Way based on the motions of orbiting satellite galaxies
). Just like we can use the orbital speeds of the planets in our solar system, along with Newton’s law of gravitation, to infer the mass of the Sun, we can use measurements of the orbits of small satellite galaxies around the Milky Way to weigh our Galaxy. ...
~ Thomas Callingham et al
This is absolutely hugely interesting! The conclusion of Thomas Callingham et al is that the mass of the Milky Way is about a trillion times the mass of the Sun.
A big question to me is how the mass of the Milky Way compares with the mass of the Andromeda galaxy, which will be very important when the two "mass centers" of the Local Group collide. Is Andromeda a lot more massive than the Milky Way? Or are these two galaxies at least relatively
equal in size?
Perseus A in the Perseus cluster. Photo: R. Jay GaBany.
Arp 271, NGC 5426 and NGC 5427.
Photo: VIMOS of ESO’s Very Large Telescope.
If the Milky Way is a flyweight galaxy compared with Andromeda's heavyweight, the collision between our two galaxies will likely scatter the Milky Way all over the place while leaving Andromeda moderately intact, perhaps somewhat similar to the collision between a smallish spiral and a giant elliptical that created the massive radio galaxy Perseus A. But if our two galaxies are relatively equal in mass, perhaps like the two components of Arp 271, NGC 5426 and NGC 5427, then the meeting of our two galaxies might be more like a meeting of equals. Of course, the results could be equally messy, if not more so.
According to Wikipedia, the mass of Andromeda may be about 150% of the mass of the Milky Way, if the mass of our own galaxy is one trillion solar masses:
Mass estimates for the Andromeda Galaxy's halo (including dark matter) give a value of approximately 1.5×1012
(or 1.5 trillion solar masses) compared to 8×1011
for the Milky Way. This contradicts earlier measurements, that seem to indicate that Andromeda Galaxy and the Milky Way are almost equal in mass.
Well, as we say in Swedish, "Den som lever får se", loosely translated as "The one who survives will live to see what happens". I guess few of us will be around to see the merging of the Milky Way and M31.